In wireless power systems, a receiver and a transmitter communicate with one another using a communication protocol. In a conventional communication protocol, the receiver requests the transmitter to increase, decrease, maintain, stop, etc., the power provided to the receiver. The communication protocol can be “in band” via for example, a load modulation technique, or be “out of band” such as via Bluetooth® of Bluetooth SIG, Inc., Wi-Fi® of the Wireless Ethernet Compatibility Alliance, etc.
Conventional communication protocol based power transfer control involves the transmitter changing its frequency across a few hundred kilo hertz (kHz). However, for some applications, it is not desirable to have a wide range of frequency of operation for wireless power transfer. Also, Federal Communications Commission (FCC) Part 15 Subpart C compliance testing becomes difficult because of varying frequency and the corresponding harmonics.
The conventional communication protocol between the receiver and the transmitter is also used to send, for example, distress signals, over voltage conditions, etc. The receiver takes considerable amount of time to send the message and the transmitter takes considerable amount of time to decipher the message and react to the sent message, therefore latency is inherent and there is a time delay. Also, the transmitter may decipher the message incorrectly, the message may be corrupted, etc., which could considerably delay the receiver in exiting from an over voltage condition. The receiver includes additional over voltage protection (OVP) circuitry that protects the receiver from excessive power during the time delay. The additional protection circuitry is rated to handle a certain amount of power, but if the power exceeds the rated power in the protection circuitry, the receiver may be susceptible to damages. Also while operating, the protection circuitry causes a rise in temperature of the receiver which is detrimental to neighboring components, for example, a battery, etc.
Metal object detection is a key safety issue in wireless power delivery. Metal objects, for example, coins, pin-clips, etc., may couple and absorb some of the magnetic flux emanating from a transmitter when placed atop or in close proximity to the transmitter. Because of the eddy currents induced, the metal objects are heated. The heated metal objects cause damage to the plastic surface of the transmitter or burn skin on contact.
Therefore, there is a long felt but unresolved need for a method and system that regulates the amount of wireless power delivered to a wireless power receiver without causing any damages to the receiver and the neighboring components of the receiver. Furthermore, there is a need for a method and a system that enable a transmitter to detect a metal object placed atop or in close proximity to the transmitter and terminate transmission of power.